The present invention is related to a metering device for utilisation with a syringe.
Metering devices serve for metering liquids and are used in biological, chemical and medical laboratories in particular. In the realisation as dispensers, they permit the stepwise delivery of a liquid from a syringe. The metering amount per delivery step can be adjustable in this. A dispenser with metering amount adjustment is known from DE 29 26 691 C2, the entire contents of which is incorporated herein by reference.
Furthermore, pipettes are known as metering devices, by which an amount of liquid defined or adjustable via the apparatus can be picked up and delivered again in one procedure.
Syringes of different sizes are frequently provided for metering devices. These have in most cases different sizes of the cross section. In the transition to another syringe size, the once set metering amount does no more coincide with the real metering amount. Metering devices have therefore become known wherein the syringe has a code which is read by a sensing device of the pipette. An analysing unit can determine the utilised syringe size and indicate the metering amount that is effectively set.
A pipette system of the mentioned kind is known from EP 0 657 216 A2, the entire contents of which is incorporated herein by reference, and from U.S. Pat. No. 5,620,661 A, the entire contents of which is incorporated herein by reference. In this pipette system, the pipette has an accommodation for a fastening portion of a syringe in a pipette casing, and in an accommodation body it has a plunger accommodation for the syringe plunger of the syringe. Moreover, there are fastening devices for reversibly fixing fastening portion and syringe plunger in their accommodations, and plunger adjustment devices for displacing the accommodation body in the pipette casing. The syringe features an information carrier with information concerning the syringe and/or its condition, and the pipette has a sensing device for the information on the information carrier. Through axial openings in their accommodations, the fastening portion and the syringe plunger are axially shiftable into the pipette to their fastening positions, the information carrier arriving in a sensing position with respect to the sensing device through this. The syringe flange has an annular collar with at least one axially directed sensing surface with an axial position as information carrier, the syringe being insertable into the pipette in different rotational positions. The sensing device is made annularly with sensors distributed over the perimeter. The sensors have elastic, compressible knobs projecting from a front side of the sensing device that faces the axial openings. Preferably, there is an analysing unit for the information read by the sensing device and a display unit for the set metering amount. There are alignment noses on the fastening portion of the syringe and guiding grooves in the accommodation for the fastening portion for reproducible alignment of the syringe with its information carrier towards the sensing device. In a practical embodiment, the syringe has plural alignment noses uniformly distributed over the perimeter of the fastening portion, which are guided on axially directed bridges on a lateral border of the accommodation in order to direct the sensing surfaces towards the sensors. The alignment noses are each one chamfered at both sides on the upside, in order to guide the bridges into the grooves between the alignment noses in case that the same are not exactly directed towards the bridges.
The pipette system allows a user to utilise the syringe type according to the practical needs and to adjust the metering amount without sumptuous conversion work. The information may also concern other specific data of the syringe and/or of the condition of the syringe, for instance the purity condition or a filling material of the syringe, which are automatically taken into account by the pipette.
In spite of the essentially rotation-blocked mounting of the syringe in the accommodation by guiding the alignment noses in the guiding groove or on the axially directed bridges, respectively, the syringes can be rotated in the accommodation when an increased force is applied. This is due to the fact that the syringes are made of a plastic material like polypropylene, so that the alignment noses are deformed under load and may be pushed out of the guiding grooves or over the bridges, respectively. The sensing surfaces may laterally hit the projecting knobs of the sensing device when the syringe is rotated, and shear the same off with the electric contacts of the sensors, so that the metering device becomes unusable. The danger of destruction of the metering device is particularly high when a high-volume syringe is rotated in the accommodation which has an adapter with a fastening portion that is detachably connected to a syringe cylinder. Because this syringe has a relatively great diameter, relatively high torques can be introduced into the fastening of the syringe. The repair is sumptuous and comprises the exchange of the relatively expensive sensing device.
Starting from this, the present invention is based on the objective to provide a metering device that is protected against damage by distortion of a syringe.